Fuel injection valve

ABSTRACT

A fuel injector for fuel-injection systems of internal combustion engines which includes an elongated, axially running, thin-walled, non-magnetic sleeve. At its downstream end, the sleeve has a bottom section, which runs substantially normal to the otherwise axial extent of the sleeve along a longitudinal valve axis. A valve needle, which is securely joined to an armature and a valve-closure member, can move axially within a feed-through opening of the sleeve. The valve-closure member cooperates with a valve-seat surface provided on a valve-seat body, the valve-seat body being pressed into the sleeve and likewise abutting, for example, on the bottom section of the sleeve. The sleeve constituted as a drawn sheet-metal part extends axially over more than half of the axial length of the fuel injector. The fuel injector is suited for applications in fuel-injection systems of mixture-compressing internal combustion engines having externally supplied ignition.

FIELD OF THE INVENTION

The present invention relates to a fuel injector.

BACKGROUND INFORMATION

U.S. Pat. No. 4,946,107 describes an electromagnetically operable fuelinjection valve, which has a non-magnetic sleeve as a connecting partbetween a core and a valve-seat body. The sleeve is securely fixed withits two axial ends to the core and to the valve-seat body. The sleevehas a constant external diameter and a constant internal diameter overits entire axial length and, accordingly, has same-size inlet orificesat both of its ends. The core and the valve-seat body are so formed withrespect to their outer diameter that they extend into the sleeve at bothends, so that the sleeve fully surrounds the two component parts, coreand valve-seat body, in these inwardly projecting areas. A valve needlemoves axially within the sleeve and has an armature which is guidedthrough the sleeve. The sleeve is permanently joined to the core and tothe valve-seat body by welding, for example, as described in GermanPatent Application No. 43 10 819, which also describes using athin-walled, non-magnetic sleeve as a connecting part between the coreand valve-seat body of a fuel injector. In terms of its structuraldesign, this sleeve corresponds substantially to the sleeve described inU.S. Pat. No. 4,946,107. The tubular sleeves make it possible to reducethe volume and the weight of the fuel injectors.

ADVANTAGES OF THE INVENTION

One of the advantages of the fuel injector of the present invention isthat it makes it possible, in a simple and cost-effective manner, tofurther diminish the volume and weight of the fuel injector and tofulfill a greater number of functions using only one sleeve-shapedcomponent part. In addition to the benefit of lower manufacturing costs,it is also simpler to assemble the fuel injector because it entailscomparatively few production steps. The present invention achieves theseadvantages by employing a thin-walled, non-magnetic sleeve as aconnecting part between a core and a valve-seat body in the fuelinjector, said non-magnetic sleeve also fulfilling the retaining,supporting or holding (seating) functions. Thus at its one axial end,the sleeve has a bottom section which runs normal to the axial extent ofthe sleeve and which assures an optimal and secure attachment of thevalve-seat body and increases sleeve stability. A major factor inreducing the volume and weight is that the sleeve extends over more thanhalf of the axial length of the fuel injector and can, therefore, evenassume the function of a fuel intake fitting.

It is also advantageous to press a valve-seat body having a valve-seatsurface into the sleeve, the bottom section of the sleeve providing acontact surface to prevent the valve-seat body from slipping.

It is further advantageous to produce the sleeve by deep drawing thesheet metal, as this method is simple and economical and, nevertheless,meets the required precision.

For “side-feed” injectors, which are partially traversed by a transverseflow, it is advantageous to provide bores or orifices in the innersleeve wall to assure a direct fuel supply to the spray orifices of thefuel injector.

One particular benefit is attained by providing the bottom section ofthe sleeve with the spray orifices for metering fuel arranged therein.This is especially cost-effective, since one can then eliminate onecomponent part (spray-orifice plate) and its associated joint.

It is also advantageous to design the sleeve to be long enough to extendover the entire axial extension length of the fuel injector. Thisenables the sleeve to assume the function of a fuel intake fitting aswell. Furthermore, the core can be easily pressed into the sleeve,making it simple to adjust the valve needle lift Moreover, the problemof seal tightness toward the interior valve space is eliminated in thislong sleeve arrangement. A top sealing ring provides a direct sealingaction on the sleeve.

Another advantage achieved by the sleeve configuration is that valveneedles or armatures of the same design can be installed for completelydifferent types of valves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a fuel injector according to thepresent invention.

FIG. 2 shows an embodiment of a sleeve according to the presentinvention.

FIG. 3 shows a first embodiment of a downstream end of the sleeve withthe valve-seat body installed.

FIG. 4 shows a first embodiment of a valve needle that can be installedin the fuel injector.

FIG. 5 shows a second embodiment of the fuel injector according to thepresent invention.

FIG. 6 shows a second embodiment of the downstream end of the sleevewith the valve-seat body installed.

FIG. 7 shows a third embodiment of the fuel injector according to thepresent invention.

FIG. 8 shows a fourth embodiment of the fuel injector in the form of aseed-feed injector.

FIG. 9 shows a second embodiment of the valve needle that can beinstalled in the fuel injector.

DETAILED DESCRIPTION OF THE INVENTION

The electromagnetically actuated valve illustrated in FIG. 1, forexample as a first embodiment in the form of an injector forfuel-injection systems of mixture-compressing internal combustionengines having externally supplied ignition, has a tubular core 2surrounded by a solenoid coil 1, and is used as a fuel intake fitting. Abobbin core 3 holds a winding of solenoid coil 1 and, in conjunctionwith core 2 having a constant outer diameter, makes it possible todesign the injector to be especially compact and short in the area ofsolenoid coil 1. Solenoid coil 1 is embedded with its bobbin core 3,e.g. in a pot-shaped magnetic housing 5, i.e., it is completelysurrounded by magnetic housing 5 in the circumferential direction andtoward the bottom. A cover element 6 that is insertable into extrudedmagnetic housing 5 assures that solenoid coil 1 is covered to the topand, thus, that solenoid coil 1 is completely enclosed, and is used forclosing the magnetic circuit. In general, this type of pot-shapedconstruction keeps magnetic housing 5, together with solenoid coil 1,dry. There is no need to provide for additional sealing.

Joined imperviously, e.g. by means of welding, to a lower core end 9 ofcore 2 and concentrically to a longitudinal valve axis 10, is a tubularand thin-walled sleeve 12 used as a connecting part, which in thiscontext with an upper sleeve section 14 partially axially surrounds coreend 9. Bobbin core 3 overlaps sleeve section 14 of sleeve 12 at leastpartially axially. Over its entire axial extent, bobbin core 3 has,namely, a larger inner diameter than the diameter of sleeve 12 in itsupper sleeve section 14. Tubular sleeve 12, e.g., of non-magnetic steel,extends downstream with a bottom sleeve section 18 to a bottom section20 that forms downstream closure of sleeve 12 and extends normal to theaxial extent of sleeve 12.

Sleeve 12 thus has a tubular form over its entire axial length, but inits entirety, together with bottom section 20, is cup-shaped. In thiscontext, over its entire axial extent to bottom section 20, sleeve 12forms a feed-through opening 21 having a substantially constantdiameter, which runs concentrically to longitudinal valve axis 10. Withits bottom sleeve section 18, sleeve 12 surrounds an armature 24 and,further downstream, a valve-seat body 25. A spray-orifice plate 26 thatis, e.g., permanently fixed to valve-seat body 25, is surrounded bysleeve 12, in the circumferential direction by sleeve section 18 and, inthe radial direction, by bottom section 20. Sleeve 12 is thus not only aconnecting part, but also fulfills retaining, supporting or holdingfunctions, in particular for valve-seat body 25, so that sleeve 12effectively also constitutes the valve-seat support. Disposed in passage21 is, e.g., a tubular valve needle 28, which is joined, e.g. bywelding, at its downstream end 29 facing spray-orifice plate 26 to,e.g., a spherical valve-closure member 30, on whose periphery areprovided, for example, five flattened areas 31 allowing the fuel to bespray-discharged to flow past.

The injector is actuated electromagnetically, e.g., in a conventionalmanner. The electromagnetic circuit includes solenoid coil 1, core 2,magnetic housing 5, and armature 24 for axially moving valve needle 28and, thus, for opening the injector against the spring force of a returnspring 33, or for closing it. Armature 24 is joined to the end of valveneedle 28 facing away from valve-closure member 30, e.g. by a weld, andis aligned to core 2. A guide opening 34 of valve-seat body 25 is usedfor guiding valve-closure member 30 during the axial movement of valveneedle 28, together with armature 24, along longitudinal valve axis 10.Moreover, armature 24 is guided during the axial movement in sleeve 12.For cost reasons, it is beneficial for magnetic housing 5 and armature24 to be manufactured from an extruded part in a lathe fixture. Coverelement 6 is, e.g., a stamped part that is fastened to magnetic housing5 by a jointed-flange connection 36, following installation of solenoidcoil 1 in magnetic housing 5.

Spherical valve-closure member 30 cooperates with a valve-seat surface35 of valve-seat body 25, said valve-seat surface 35 taperingfrustoconically in the direction of flow and being formed in the axialdirection downstream from guide opening 34. At its front end facing awayfrom valve-closure member 30, valve-seat body 25 is concentrically andsecurely joined to, e.g. saucer-shaped spray-orifice plate 26, e.g., bya weld, as shown in FIG. 3.

Inserted into a graduated flow-through bore 43 of core 2 that runsconcentrically to longitudinal valve axis 10 and is used for supplyingfuel in the direction of the valve seat, in particular of valve-seatsurface 35, is an adjusting sleeve 45. Adjusting sleeve 45 is used foradjusting the resilience of return spring 33 that adjoins it, saidreturn spring 33, in turn, being braced with its opposite side againstvalve needle 28.

The depth of insertion of valve-seat body 25 having saucer-shapedspray-orifice plate 26 is decisive, among other things, for the lift ofvalve needle 28. It is essentially already set by the spatial positionof bottom section 20 of sleeve 12. In this context, the one end positionof valve needle 28 is defined, given a de-energized solenoid coil 1, bythe valve-closure member's 30 contact making on valve-seat surface 35 ofvalve-seat body 25, while the other end position of valve needle 28,given an energized solenoid coil 1, results from armature's 24 contactmaking on core end 9. To prevent magnetic sticking, provision can bemade between armature 24 and core end 9 for a limit-stop washer 47 made,e.g. of a non-magnetic, wear-resistant, hard-rolled material. Thus, onecan then prevent the surfaces of core 2 and armature 24 from beingcoated (e.g., chromized) in their limit-stop areas. The limit-stop areason core 2 and armature 24 are cold work-hardened and compressed in asmoothing-rolling operation. Moreover, the lift is adjusted by axiallyshifting core 2 in upper sleeve section 14 of sleeve 12, said core 2being pressed in with little (not substantially tight) interference.Core 2 is then securely joined in the appropriate, desired position tosleeve 12, a laser weld being useful on the periphery of sleeve 12. Thejointing excess (interference) of the press fit can also be selected tobe large enough to absorb any occurring forces and to guarantee completeseal tightness, thus making it possible to eliminate a weldingoperation.

A fuel filter 52 projects into the inflow end of flow-through bore 43 ofcore 2 and assures that those fuel components are filtered out, which,because of their size, could block or damage the injector. The readyadjusted injector is substantially enclosed by a plastic extrusion coat55, which starts out from core 2, extending axially over solenoid coil 1up to sleeve 12, and even extends downstream past bottom section 20 ofsleeve 12, an electrical plug connector 56 also being extruded on alongwith said plastic extrusion coat 55. Solenoid coil 1 is electricallycontacted and, thus, energized via electrical plug connector 56.

Using the relatively inexpensive sleeve 12 makes it possible for one todo without the lathed parts customarily found in injectors, such asvalve-seat supports or nozzle holders, which, because of their largerouter diameter, are more voluminous and more expensive to manufacturethan sleeve 12. In FIG. 2, sleeve 12 of the first embodiment shown inFIG. 1 is depicted as a single component part on a different scale.Thin-walled sleeve 12 is formed, e.g., by deep-drawing, a non-magneticmaterial, such as rust-resistant CrNi steel being used as a material.Sleeve 12 constituted as a drawn sheet-metal part is used, as describedabove, because of its large extent, for accommodating valve-seat body25, spray-orifice plate 26, valve needle 28 with armature 24, returnspring 33, as well as at least partially core 2 and, consequently, alsothe lift-limiting limit-stop area of armature 24 and core 2. In itsbottom section 20, the sleeve 12 has a centrally disposed outlet orifice58 with a diameter large enough to allow the fuel that isspray-discharged through spray orifices 39 of spray-orifice plate 26 toleave the injector unimpeded. If the intention is to use sleeve 12 in a“seed-feed” injector, as shown in FIG. 8, then provision can easily bemade in sleeve 12 for inlet orifices 59, which permit fuel to enter intothe interior of sleeve 12. The top-feed injector shown in FIG. 1 has asleeve 12 that does not have any inlet orifices 59, since the fuelenters along longitudinal valve axis 10, axially via flow-through bore43, into sleeve 12. At its axial end opposing bottom section 20, sleeve12 has, for example, a peripheral rim 60 that is bent slightly radiallyto the outside. Peripheral rim 60 is formed by dissociating spillover(excess) material during the deep-drawing process. The preassembledsubassembly includes solenoid coil 1, bobbin core 3, magnetic housing 5and cover element 6 is slid axially onto the periphery of sleeve 12, adelimiting effect by peripheral rim 60 and a clamping of cover element 6in the assembled state being possible. Bobbin core 3, magnetic housing5, and cover element 6 all have centrally disposed feed-throughopenings, through which sleeve 12 then extends.

FIGS. 2 and 3 show bottom sleeve section 18 and bottom section 20,together with an installed valve-seat body 25, as well as with aspray-orifice plate 26 attached thereto. Besides a bottom part 38, towhich valve-seat body 25 is secured and in which run at least one, (e.g.four), spray-discharge orifice 39 formed through erosion or stamping,saucer-shaped spray-orifice plate 26 also has an upstream,circumferential retention rim 40. Retention rim 40 is bent upstreamconically outwardly, so that it abuts on the inner wall of sleeve 12defined by feed-through opening 21, a radial pressing (squeezing) beinggiven. Valve-seat body 25 is pressed in cold into sleeve 12 and is notwelded. The pressing, e.g. into feed-through opening 21 of sleeve 12, iscarried out until spray-orifice plate 26, which is secured, e.g., bywelding to valve-seat body 25, abuts with its bottom part 38 on bottomsection 20 of sleeve 12. At its end, retention rim 40 of spray-orificeplate 26 has a slightly larger diameter than the diameter offeed-through opening 21 of sleeve 12, so that retention rim 40 pressesat its end against sleeve 12, thus in addition to pressing in valve-seatbody 25, safeguards against a slipping of valve-seat body 25.

As an alternative to sleeve-shaped valve needle 28 shown in FIG. 1,another embodiment of a valve needle 28 in the injector is shown by FIG.4. In this embodiment, valve needle 28 is designed as an oblong, solidcomponent. Thus, it is no longer possible for the fuel to be suppliedwithin valve needle 28 in the direction of valve-seat surface 35.Therefore, provision is already made in armature 24 for outlet orifices62′, through which the fuel arriving from an inner orifice 63 ofarmature 24 can flow, to then arrive outside of valve needle 28, furtherdownstream, in feed-through opening 21 of sleeve 12. Armature 24 has,e.g., a stepped design, a top, upstream armature section 64 having alarger diameter than a bottom downstream armature section 65. Opening 63running inside of armature 24 has a smaller cross-section in bottomarmature section 65 than in top armature section 64. Outlet bores 62′are provided, e.g., as radially running transverse bores in the wall ofbottom armature section 65. A permanent connection of armature 24 andvalve needle 28 is achieved, e.g., in that armature 24 is pressed ontoupstream end 66 of valve needle 28, since there is an interference fitbetween valve needle 28, at least at its end 66 to be pressed in, andorifice 63. Provision is made at end 66 of valve needle 28, for example,for a few circumferential, e.g., crimped grooves 67, which are used forlatching armature 24 after it has been pressed on valve needle 28.

After the press-in operation, valve needle 28 extends with its end 66only so far into orifice 63 that outlet orifices 62′ still remaincompletely free. An alternative jointing method, however, is the laserwelding operation (shown in FIG. 1). Valve needle 28 and sphericalvalve-closure member 30 are permanently joined, e.g., by the laserwelding operation, valve needle 28, at its downstream end facing awayfrom armature 24, having an upset, collar-shaped attachment flange 68.Attachment flange 68 is formed to conform to the radius of sphericalvalve-closure member 30.

The fuel injector shown in FIG. 5 substantially corresponds in its basicdesign to the injector shown in FIG. 1. Therefore, the following willonly describe those components or subassemblies having a differentdesign. Parts that have remained the same or that have equivalentfunctions as those in FIG. 1 are characterized by the same referencesymbols in all further exemplary embodiments. In place of magnetichousing 5, solenoid coil 1 is surrounded by at least one conductiveelement 70 designed, e.g., as a bracket and being used as aferromagnetic element. Conductive element 70 circumferentially surroundssolenoid coil 1, at least partially, and fits with its one end on core 2and with its other end on sleeve 12, e.g., in the area of top sleevesection 14, and is able to be joined to sleeve section 14, e.g., bymeans of welding, soldering, or cementing. Another distinguishingfeature lies in the embodiment of armature 24. In contrast to armature24 shown in FIG. 4 whose outlet bores 62′ run radially, outlet bores 62″are now designed to run axially and, to be specific, in a transitionregion 72, which represents a step between top armature section 64 andbottom armature section 65.

The important distinction pertains, however, to the design of sleeve 12.The stepped, thin-walled, non-magnetic sleeve 12, e.g., is so designedthat top sleeve section 14 guiding armature 24 has a slightly largerdiameter than bottom sleeve section 18, feed-through opening 21 ofsleeve 12 being reduced to the same extent in the downstream direction.Moreover, bottom section 20 of sleeve 12 assumes the functions of aspray-orifice plate, so that spray-orifice plate 26 can be omitted.Similarly to the known spray-orifice plates, base section 20 has atleast one, e.g., four spray orifices 39, which are introduced, e.g., bymeans of stamping or erosion.

As shown in FIG. 6, which conforms to FIG. 3, valve-seat body 25 andsleeve 12 are again shown on an enlarged scale in the area of bottomsection 20. Bottom section 20 is designed as a conventionalspray-orifice plate and, thus, does not have any outlet orifice 58, butrather only spray orifices 39 for metering the fuel. In addition to theconnecting, holding and supporting functions already described, sleeve12 now also fulfills a metering and spray-discharge function. Valve-seatbody 25 can either be imperviously welded to sleeve 12 in the area ofbottom section 20 and/or in the area of bottom sleeve section 18, or bepressed imperviously into sleeve 12. The benefit of this arrangement isthat it eliminates the need for one component (spray-orifice plate 26),as well as for at least one joint. Moreover, sleeve 12, together withsaid bottom section 20, is rendered more rigid, lessening the risk ofdamage to the valve components during handling.

While in the preceding embodiments, sleeve 12 always extended overapproximately ⅔ of the injector's length, the injector shown in FIG. 7uses, as a valve base, a sleeve 12 which itself predefines the length ofthe injector and, thus, also runs nearly over the entire length of theinjector. The advantage of sleeve 12 that traverses the injector is thatthere is no longer a need for joints that adversely affect sealtightness. Therefore, a laser welding on sleeve 12 is not necessary,because a top sealing ring 74 provides a direct sealing action on sleeve12. Moreover, the lift adjustment can be carried out very easily. Forthis, core 2 is pressed so far into sleeve 12 from the inflow end of thefuel injector until the lift of valve needle 28 reaches the desiredmagnitude. After that, the adjusted lift is no longer negativelyinfluenced by other assembly steps. As an alternative to the versionshown in FIG. 7, bottom section 20 can also directly have spray orifices39 (compare FIGS. 5 and 6).

The injector is easily assembled, e.g., in that first solenoid coil 1,magnetic housing 5, and cover element 6 (or optionally at least oneconductive element 70) are mounted on sleeve 12, plastic coat 55 is thenextrusion-coated on, valve-seat body 25 is subsequently pressed intosleeve 12, and valve needle 28, together with armature 24, areintroduced, and core 2 is then pressed in so far until the nominal liftis reached. All of the subsequent assembly steps are alreadysufficiently known. Sleeve 12 is designed, e.g., so as to be steppedtwice over its axial length, the cross-section of feed-through opening21 being reduced slightly in each case in the downstream direction. Thesteps provided, e.g., in the limit-stop area of armature 24 and core 2,as well as above core 2 facilitate assembly.

FIGS. 8 and 9 show that a sleeve 12 according to the present inventioncan also be installed in completely different valve types, e.g., in“side-feed” injectors. A further description of such injector will notbe provided, as it is already known, at least in terms of its basicdesign, from the German Patent Application No. 39 31 490 and can begleaned from there. Valve needle 28 shown in FIG. 9 includes a nozzlepintle 76 that extends into a centrally disposed valve-seat body bore 75of valve-seat body 25 can have a simplified design as compared to knownvalve needles of comparable injectors by providing only one guidesection 77. Usually such valve needles have two guide sections 77.Moreover, valve needle 28 is guided through armature 24 in sleeve 12. Asalready shown in FIG. 2, for applications in side-feed injectors, sleeve12 can have at least one inlet orifice 59, via which fuel is supplied inthe direction of valve-seat surface 35.

What is claimed is:
 1. A fuel injector for a fuel-injection system of aninternal combustion engine, comprising: a valve-seat body; a valve seatsituated on the valve-seat body; a thin-walled axially-extendingnon-magnetic sleeve including a bottom section at a downstream end ofthe sleeve, the bottom section extending substantially normal to thesleeve, the valve-seat body being axially and radially surrounded by thesleeve; and a valve needle including a valve-closure member, the valveneedle being axially movable in the sleeve along a longitudinal valveaxis of the fuel injector and cooperating with the valve seat.
 2. Thefuel injector according to claim 1, wherein the sleeve has a first axiallength that is more than half of a second axial length of the fuelinjector.
 3. The fuel injector according to claim 1, wherein the sleeveincludes a drawn sheet-metal part.
 4. The fuel injector according toclaim 1, wherein the valve-seat body is pressed into the sleeve, thevalve-seat body including a bottom section and an axially running bottomsleeve section for contacting the sleeve.
 5. The fuel injector accordingto claim 1, wherein the sleeve includes an axially extending wall, thewall having at least one inlet orifice.
 6. The fuel injector accordingto claim 1, wherein the bottom section has an outlet orifice, andwherein fuel pre-metered upstream from the bottom section flows throughthe outlet orifice and emerges unimpeded.
 7. The fuel injector accordingto claim 1, wherein the bottom section has an outlet orifice, andfurther comprising: a spray-orifice plate securely joined to thevalve-seat body at a body downstream end of the valve-seat body andincluding at least one spray orifice, the spray-orifice plate at leastpartially contacting on the bottom section, the at least one sprayorifice cooperating with the outlet orifice.
 8. The fuel injectoraccording to claim 1, wherein the bottom section has at least one sprayorifice to generate a fuel-metering effect.
 9. The fuel injectoraccording to claim 1, wherein the sleeve includes a feed-through openingand at least one step to form a stepped shape extending along an axiallength of the sleeve, the feed-through opening having a diameter beingreduced with each of the at least one step in a downstream direction.10. The fuel injector according to claim 1, wherein the sleeve extendsalong an axial length of the fuel injector.
 11. The fuel injectoraccording to claim 1, further comprising: a coat surrounding the sleeve.12. The fuel injector according to claim 11, wherein the coat is aplastic extrusion coat.
 13. The fuel injector according to claim 1,further comprising: a magnet core arranged inside the sleeve; anarmature arranged inside the sleeve; a magnet coil arranged outside ofthe sleeve; and a magnetic housing arranged outside of the sleeve,wherein the magnet coil, the armature and the magnetic housing form anelectromagnetic circuit for axially moving the valve needle, and themagnetic housing is arranged outside of the magnet coil.
 14. The fuelinjector according to claim 1, wherein: the sleeve has a first axiallength that is more than half of a second axial length of the fuelinjector; and the sleeve includes a drawn sheet-metal part.
 15. The fuelinjector according to claim 1, wherein: the valve-seat body is pressedinto the sleeve, the valve-seat body including a bottom section and anaxially running bottom sleeve section for contacting the sleeve; and thesleeve includes an axially extending wall, the wall having at least oneinlet orifice.
 16. The fuel injector according to claim 1, wherein: thesleeve has a first axial length that is more than half of a second axiallength of the fuel injector; the sleeve includes a drawn sheet-metalpart; the valve-seat body is pressed into the sleeve, the valve-seatbody including a bottom section and an axially running bottom sleevesection for contacting the sleeve; and the sleeve includes an axiallyextending wall, the wall having at least one inlet orifice.
 17. The fuelinjector according to claim 16, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 18. The fuel injector according to claim16, further comprising: a magnet core arranged inside the sleeve; anarmature arranged inside the sleeve; a magnet coil arranged outside ofthe sleeve; and a magnetic housing arranged outside of the sleeve,wherein the magnet coil, the armature and the magnetic housing form anelectromagnetic circuit for axially moving the valve needle, and themagnetic housing is arranged outside of the magnet coil.
 19. The fuelinjector according to claim 18, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 20. The fuel injector according to claim1, wherein the bottom section includes an outlet orifice, and fuelpre-metered upstream from the bottom section flows through the outletorifice and emerges unimpeded, and further comprising: a spray-orificeplate securely joined to the valve-seat body at a body downstream end ofthe valve-seat body and including at least one spray orifice, thespray-orifice plate at least partially contacting on the bottom section,the at least one spray orifice cooperating with the outlet orifice, theat least one spray orifice providing a fuel-metering effect.
 21. Thefuel injector according to claim 20, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 22. The fuel injector according to claim20, wherein: the sleeve has a first axial length that is more than halfof a second axial length of the fuel injector; the sleeve includes adrawn sheet-metal part; the valve-seat body is pressed into the sleeve,the valve-seat body including a bottom section and an axially runningbottom sleeve section for contacting the sleeve; and the sleeve includesan axially extending wall, the wall having at least one inlet orifice.23. The fuel injector according to claim 22, wherein a plastic extrusioncoat directly surrounds the sleeve.
 24. The fuel injector according toclaim 20, further comprising: a magnet core arranged inside the sleeve;an armature arranged inside the sleeve; a magnet coil arranged outsideof the sleeve; and a magnetic housing arranged outside of the sleeve,wherein the magnet coil, the armature and the magnetic housing form anelectromagnetic circuit for axially moving the valve needle, and themagnetic housing is arranged outside of the magnet coil.
 25. The fuelinjector according to claim 24, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 26. The fuel injector according to claim22, wherein: the sleeve includes a feed-through opening and at least onestep to form a stepped shape extending along an axial length of thesleeve, the feed-through opening having a diameter being reduced witheach of the at least one step in a downstream direction; and the sleeveextends along an axial length of the fuel injector.
 27. The fuelinjector according to claim 26, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 28. The fuel injector according to claim22, further comprising: a magnet core arranged inside the sleeve; anarmature arranged inside the sleeve; a magnet coil arranged outside ofthe sleeve; and a magnetic housing arranged outside of the sleeve,wherein the magnet coil, the armature and the magnetic housing form anelectromagnetic circuit for axially moving the valve needle, and themagnetic housing is arranged outside of the magnet coil.
 29. The fuelinjector according to claim 28, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 30. The fuel injector according to claim28, wherein: the sleeve includes a feed-through opening and at least onestep to form a stepped shape extending along an axial length of thesleeve, the feed-through opening having a diameter being reduced witheach of the at least one step in a downstream direction; and the sleeveextends along an axial length of the fuel injector.
 31. The fuelinjector according to claim 30, wherein a plastic extrusion coatdirectly surrounds the sleeve.
 32. The fuel injector according to claim1, wherein a plastic extrusion coat directly surrounds the sleeve.